Signal voltage regulator for power line high-frequency transmitters



Sept. 9, 1952 N, c o 2,610,241

SIGNAL VOLTAGE REGULATOR FOR POWER LINE HIGH-FREQUENCY TRANSMITTERS Filed April 13, 1951 Znmcntor 7 ROBERT N. EICHORN BY '1 W agent Patented Sept. 9, 1952 SIGNAL VOLTAGE REGULATOR FOR POWER LINE HIGH-FREQUENCY TRANSMITTERS Robert N. Eichorn, Johnson City, N..Y., assignor to International Business Machines Corporation, New York, N. Y., a corporation of New York Application April 13, 1951, Serial No. 220,953

4 Claims.

The present invention relates to signal voltage regulating means and more particularly to a means for limiting the output voltage of signal transmitters used in regulating electric time systems. r

Electric time systems that are governed by electronic regulation make use of an electronic supervisory signal to test automatically for synchronism of individual synchronous motor-driven time indicating clocks with a master control clock every hour! This is accomplished by allowing the master control clock toturn an electronic transmitter on hourly causing it to transmit a supervisory carrier current signal. The transmitter is connected to a local alternating current power system and the transmittedsignal is available for any selective tuned electronic receiving units such as time indicating "clocks equipped with electronic receivers and which may be connected to conventional lighting cir cuits.

In some time system installations transmitters are used which in addition to sending a supervisory signal may also send upwards to three additional carrier current frequencies which may be used to energize audible signal devices such as bells or buzzers which may be connected in the lighting circuits along with the time indicating clocks. This type of arrangement is generally found in most school installations.

In such school installations it is often neces sary to install the signal transmitter at a considerable distance, such as fifty feet or more, from the lighting power transformer. impedance of the power circuit to exceed recommended limits of variation. This high impedance increases the signal voltage due to the decreasing shunt-effect of the transformer secondary winding and permits signal dissipation principally by the load rather than by the transformer. Consequently when the time system is operating under a nearly no-load condition the signal causes cross-channel interference particularly in the receiver units which are located nearest to the transmitter. n

Accordingly it is the principal object of the invention to provide in an electric time system an automatic methodof loading the secondary illustrated in the accompanying drawing, which discloses, by way of example, the principle of This causes the 2 v. the. invention and the contemplated, of applying that principle.

In the accompanying drawing the single figure is a circuit diagram of a signal system embodying the invention and shows schematically only suflicient equipment of a standard electric time system to enable the invention to be understood.

The operation of the standard electric time system to which the invention is applied will first over the three-phase high tension conductors HTI, HT2 and HT3which are delta-connected to the primary of the power transformer PT.

The secondary of this transformer is Y-connected to bus bars which serve to distribute power to the'low tension leads I, 2, and 3. The neutral point of the Y connection is connected to a bus bar which is connected to the neutral con-,-

ductor N. The various time indicating clock units and audible signal devices are connected between any one of the phase leads and the neutral conductor. These time indicating clock units, sometimes referred to as secondary clocks,

are well-known and it will suffice for purposes of 1 the present invention to but briefly describe their operation.

The clocks are operated by a continuous running synchronous motor which may receive power from the power transformer PT of a conventional lighting circuit. Each clock is provided with anelectronic receiver which may be tuned to receive supervisory signals from asignal transmitter TR for the purpose of time correction.

The supervisory signal from the transmitter is fed over the same power system which supplies the power for operating the synchronous motors of the clocks. Upon receipt of the supervisory signal a clutch magnet is energized which will trip a suitable latch type clutch device and there by operate in conjunction with the synchronous motor to drive the clock hands through a correction cycle. The clocks may have otherreceiver units which may be tuned to receive audible signals from thetransmitter TR, to operate a buzzer or bell. In the absence of any super visory signal the clocks willrun as an ordinary synchronous motor wall clock. a n

The transmitter TB, is a conventional type signal transmitter consisting of a power supply, an"

oscillator section, an amplifiersection and i an output section. It is capable of transmitting four different carrier current frequencies', one

best mode, which has been amplifying circuit to provide a usable-signal.

having the desired frequency and considerable power. tapped secondary of an open core output transformer OT which is connected to the alternating current distribution system through coupling capacitors.

The master time control device TC may be the conventional type of master clock which is used to regulate time indicating clocks. The master clock includes a marine escapement clock movement which is driven by a synchronous motor connected to a two line source of alternating current. Suitable cam controlled contacts are operated by the clock movement to emit a corrective signal to the transmitter TR'once each hour. This signal is of four seconds duration and is transmitted two seconds before the 58th minute to'two seconds after the 58th minute' The time system installation to which the present invention is applied is schematically shown in the drawing and it should be noted that in this type of installation the bus bars are rather remotely located from the power transformer PT. This is a typical condition in some schools where the power distribution panel may be located in the basement of the schoolbuilding and the power transformer may be located several hundred feet away on a pole. The bus bars distribute power, by means of'the usual feeder lines, to the various loads L which may be the school lights, electric ovens in a home making class room, electric heaters, etc., as well as the-secondary clocks and bells or buzzers of the time system.

The transmitter output signal appears across the secondary of the tapped output transformer OT which is coupled through capacitors to the" bus bars of the local power system. To obtain the maximum transmitter signal power transfer to the distribution sys'tem,'the impedance of the transmitter is properly matched to the load impedance by selecting various tap connections to' the transmitter output transformer. An optimum impedance match is obtained when the output signals are near the same level for all frequencies.

It has been determined that in such a system where the transmitter sends a plurality of signals-of different frequencies, if the signal strength should exceed a predetermined voltage it may cause cross-channel operation because of the inability ofan individual receiver to reject a signal .on an adjacent channel.

Past experience has shown that cross-channel interference can occur in systems where the transmitter is connected to the lighting power system more than approximately fifty feet .from the power transformer especially during a nearly no-load operation when the load, such as the school lights, heaters, etc, is removed from the power'system causing thetransmitter output sig-' nals to increase in'voltage.v Since the reflected impedance .of the power transformer secondary winding is high at the remote point of signal in-.

The amplified signal is put across the sertion, the high signal voltage is dissipated principally by the load rather than by the transformer winding and interference may result.

' on'dary side of the output transformer of the transmitter whenever the signal voltage exceeds a certain predetermined voltage. The resistance serves to limit the output signal voltage delivered to the individual receiver units to the value of r the predetermined voltage or less.

Referring to the drawing, the wires I0 and II are arranged to bring power from the bus bars to the volt power input terminals I2 of the master time control device TC. Also wires I3 and I4 are connected between said wires I0 and I I and the power input terminals I5 of the transmitter TR to heat the various tube filaments present in the well-known oscillator and amplifier sections therein and to make rectified high voltage available for the keying operations;

When the time control device TC keys the transmitter TR over the control wires I6 a signal will be superimposed on the 110 volt lines I! and I8. The signal will be distributed throughout the clock system and fed back over the wires I0 and II to the input terminals I5 of the transmitter TR'and superimposed on a pair of wires I9 and 20 connected to said terminals I5. Connected across wires I 9 and 20 is a series resonant'circuit comprising coils 2I, 22 and'capacitor 23. The coils are of the powdered iron adjustable core type and are tuned so that the resonant combination oilers high impedance to all unwantedfrequencies and minimum impedance'to the desired frequency.

Inductively coupled to the coil 2I is a coil 24 which is connected between the starteranode and the cathode of a three-electrode cold cathode gas discharge tube CCT. A capacitor 25 is connected between the starter anode and the cathode of tube GOT to form a parallel resonant combination with the coil 24. The coils 2| and 24 are inductively coupled so that a signal in excess of a predetermined voltage will result in suflicient voltage being developed across the parallel resonant combination and starter anode to cause tube GOT to conduct. Whentube CCT conducts, a relay coil 26 will be energized.

A coil 21, wound on the same core as coil H,

is connected by the leads 28' and 29 to experi-- mentally determined taps of the output trans-- former secondary winding. Also included in this circuit is a suitable resistance 30 and the nor mally open points 26a of relay 26. It follows then that when relay'26 is energized due to an ex cessive signal, the normally open relay pointsv 26a will close causing the coil 21 to be-energized and placing the resistance 30' across the taps of'the secondary winding of the output transformer to decrease the 'output signal voltage. A

coil 2 I, sufficient voltage will be induced through. coil-24 to sustain tube CCT in a conductive state; for the duration of the transmitted signal. This 4 condition is desirable as tube 001 would otherwise alternately extinguish and reignite whenever the contacts 26a placed the load 30 across the output winding and reduced the signal voltage. This would cause relay 2G to chatter.

The coil 22 is wound on the same core as coil 24 to provide a closer coupling and to keep the sensitivity relatively uniform over the range of signal frequencies used.

While there have been shown and described and pointed out the fundamental novel features of the invention as applied to a preferred embodiment, it will be understood that various omissions and substitutions and changes in the form and details of the device illustrated and in its operation may be made by those skilled in the art, without departing from the spirit of the invention. It is the intention, therefore, to be limited only as indicated by the scope of th following claims.

What is claimed is:

1. In a signalling system having a power source and a transmitter connected to said power source including an output transformer and means for generating high frequency signals in said transformer, signal voltage regulating means comprising a series resonant circuit responsive to signals generated by the transmitter, a three-electrode cold cathode gas discharge tube, a parallel resonant circuit connected to the starting electrode of said tube and inductively coupled to said series resonant circuit for causing said tube to conduct when said series resonant circuit responds to a signal which is above a predetermined voltage level, a relay connected in circuit to the main electrodes of said tube, a resistance circuit adapted to be connected across the secondary of the transmitter output transformer, and contacts in said resistance circuit under control of said relay for connecting said resistance circuit to effect a decrease in the output signal voltage of the transmitter to at least the predetermined voltage level.

2. In a signalling system having a power source and a transmitter connected to said power source including an output transformer and means for generating high frequency signals in said transformer, signal voltage regulating means comprising a three-electrode cold cathode gas discharge tube connected in circuit across the power input terminals of the transmitter, a series resonant circuit having a first coil, a second coil and a capacitor connected in series and tuned to a desired signalling frequency, a parallel resonant circuit connected between the starter electrode and the cathode of said tube, a coil in said parallel resonant circuit inductively coupled to said first coil of said series resonant circuit so that signals above a predetermined voltage level will develop sufficient voltage in said parallel resonant circuit to cause said tube to conduct, a circuit adapted to be connected across the secondary of the transmitter output transformer and including a resistor and a pair of contacts, and a relay connected in said tube circuit for controlling said contacts to connect said last named circuit to effect a decrease in the output signal voltage of the transmitter to at least the predetermined voltage level.

3. Signal voltage regulating means according to claim 2 which includes a coil in the circuit connected across the secondary of the transmitter output transformer, said coil being inductively coupled to the first coil of said series resonant circuit to sustain operation of said tube for the duration of the transmitted signal.

4. Signal voltage regulating means according to claim 2 characterized by having the coil in said parallel resonant circuit inductively coupled to the second coil in said series resonant circuit to keep the sensitivity relatively uniform over the range of signal frequencies used.

ROBERT N. EICHORN.

No references cited. 

